Inkjet printing systems are extensively used throughout the world for the reproduction and generation of text and images. Inkjet printing systems eject liquids in the form of droplets that are deposited upon a suitable receiver in an image-wise fashion. Common uses include the printing of text and the reproduction of images. Liquids that are ejected can be inks or pigments and the applications vary widely but include printers, plotters, facsimile machines and copiers. For purposes of convenience the concepts of this invention are discussed in the terms of a thermal inkjet printer that employ one or more supplies or reservoirs of liquids to be deposited upon a medium such as paper.
Ink is supplied to a liquid ejector mechanism, also known as a print head, through a supply channel and into a chamber of the liquid ejector that contains thermal resistors as firing mechanisms. Sending an electrical current through the thermal resistors causes the heating of the resistor and forces the formation of a vapor bubble within the chamber. The expanding vapor bubble within the chamber then causes an ink droplet to be forced out of an orifice situated upon the chamber. As ink is expelled from the orifice, energy is removed from the thermal resistor, the bubble collapses and ink refills the chamber to begin another sequence.
As the need for ejection speed increases, so does the optimization of the operation of the chambers to maximize ink flow. Additionally the throughput requirement also means the need for more chambers and ejection orifices. It is a constant engineering challenge to maintain the proper balance that is required to enhance inkjet system performance.
In typical inkjet printing systems, a filter element is generally placed at the inlet to the supply port of an inkjet chamber. Reference U.S. Pat. No. 6,582,064 by Cruz-Uribe et al., of Hewlett-Packard Company, Houston Tex., that describes integrated fluid filters constructed from stacks of stacked thin film layers with openings that function as filters. Reference also U.S. Pat. No. 6,502,927 by Nozawa of Canon Kabushiki Kaisha of Tokyo, Japan that describes pillars as filters. These filters have several functions such as that of an ink conduit and function to preclude the delivery of impurities, debris and air bubbles that could enter the chamber of a liquid ejector and cause clogging of the chamber or orifice thus rendering a firing chamber inoperable.
Chambers and geometries are commonly configured to enhance operational performance. Reference U.S. Pat. No. 6,478,410 by Prasad, et al. of Hewlett-Packard Company, Palo Alto, Calif. that attempts to balance a higher inkjet droplet generator density with structures that attempt to achieve proper control of ink flow. Reference also U.S. Pat. No. 6,601,945 by Kitakami of Canon Kabushiki Kaisha, of Tokyo, Japan that attempts to correct for image quality by using a “windshield liquid droplet” that prevents the displacement upon a recording medium of the ink droplet discharged in a high density “full discharge” mode even when the ink droplet has a fine volume.
U.S. Pat. No. 5,734,399 by Weber et al. of Hewlett-Packard Company of Palo Alto Calif. discloses shaped barrier geometries that prevent stray particles from reaching ink feed channels. The barriers are configured to have a plurality of inner barrier islands each associated with a chamber and a particular heater resistor. These barrier islands commonly occupy a common area between the ink firing chamber and the ink plenum, commonly known as an ink supply.
U.S. Pat. No. 6,540,335 by Touge et al. of Canon Kabushiki Kaisha of Tokyo, Japan discloses an ink jet printhead for preventing problems that are caused by air bubbles caught in the printhead. Bubbles are left in the printhead after liquid discharge, and the invention enables the ejection of droplets with high reliability by controlling the residual bubble.
U.S. Pat. No. 6,137,510 by Sato et al. of Canon Kabushiki Kaisha of Tokyo, Japan discloses the additions of pluralities of ribs that provide increased mechanical strength to the orifice plate and additionally reduce the detrimental effects of air bubbles. These ribs reduce the effects of these retained bubbles thereby achieving reliable ink droplet discharge.
Lastly, U.S. Pat. No. 6,158,843 by Murthy et al. of Lexmark International of Lexington, Ky., discloses pillars extending vertically into the firing chamber but not into the common area.
Filter elements also play an important role in the hydraulic interactions between neighboring nozzles. As the inkjet recording process has matured over the years, so too has the demand for ink jet recording heads to achieve higher recording speeds. Pluralities of nozzles that reside adjacent one another within a given printing system have to be addressed in relationship to one another within a short period of time. As these blocks of nozzles are fired, the stability within adjacent unfired or recently fired nozzles is negatively affected, thereby substantially increasing the interaction between adjacent nozzles. The generation of this adverse hydraulics, coupled with the internal filtering elements, affects the chamber refill time and limits how quickly a particular chamber can be ready to be reused. Since the chamber refill time is directly proportional to how quickly a chamber can be fired, the matching of filter properties is important. Properties that improve the refill efficiencies and additionally satisfy the need to filter impurities such as dust is critical, and most prior art suggests that attempts at doing both well have not been entirely successful.